branchial clefts

Definition: a bilateral series of slitlike openings into the pharynx through which water is drawn by aquatic animals; in the walls of the clefts are the vascular gill filaments that take up oxygen from the water passing through the clefts; sometimes wrongly applied to the pharyngeal grooves of mammalian embryos, which are imperforate, rudimentary homologues of complete gill clefts.